NetApp CEO Dan Warmenhoven and co-founder Dave Hitz discussed the suit on a conference call Wednesday, stressing that they are "not interested in going after ZFS users." In a blog, Hitz called Sun's ZFS file system "a conscious reimplementation of our WAFL filesystem, with little regard to intellectual property rights."

NetApp said in a press release that it is filing the suit "in the wake of prolonged and aggressive claims" by Sun. Sun inherited the dispute when it acquired StorageTek two years ago.

"Sun's aggressive demand that we license some of their IP caused us to examine carefully whether we were infringing their IP rights and whether they might be infringing ours," NetApp said. As a result of that review, NetApp said it "believes Sun unfairly distributes ZFS technology to third parties to induce the adoption and distribution of the infringing technology in their products without informing them of applicable NetApp patents."

NetApp said it made "major efforts" to resolve the issues, but Sun "shifted from an aggressive position to not being responsive, leaving important issues unresolved. To remove any doubts, NetApp has turned to the courts."

In a statement late Wednesday, Sun responded that NetApp's lawsuit "is a clear indication that NetApp considers Sun technology a threat, and is a direct attack on the open source community. ... Many of the claims raised in the lawsuit are factually untrue. For example, it was NetApp who first approached Sun seeking to acquire the Sun patents NetApp is now attempting to invalidate. It is unfortunate that NetApp has now resorted to resolving its business issues in a legal jurisdiction (East Texas) long favored by 'patent trolls.'

"Bottom line, Sun indemnifies its customers, and stands behind the innovations we deliver to the marketplace."